Encounters was a good learning environment. Simple, short, linear adventures, 1 encounter/1-hr session, open entry/exit, fairly low-pressure. New players would graduate to DMing adventures like that very quickly.
AL adventures are more varied, some short, some linear, some sandbox, which is nicer from another PoV.
But I'm not so sure about the focus on AP. Maybe it's a good moneymaker, but shorter modules would seem better for early-DM experiences. I think one reason LMoP gets so much love is that it is fairly short.
It's easier to write a quality shorter adventure IMHO. It's also hard to get people to care about the end vs meeting a short term goal.
They tried AL here didn't work. DMs didn't go for it.